Cartilage defects are a main issue in orthopedics to which there is no known physiological treatment to restore the identical tissue. Because of the ever increasing elderly population with osteoarthritic disease and an estimated 1 million or more total joint arthroplasties performed annually in the United States, cartilage defects remain a major concern in orthopedics and there is a strong need to resolve this cartilage repair problem.
Cartilage tissue engineering remains a challenge because cartilage does not heal itself spontaneously as it does not contain blood vessels. The main cells of cartilage, chondrocytes, are limited in self repair. The low density of cells, which do not replicate, hide among a dense isolating extracellular matrix. This leads to a lack of regeneration ability because the cells are cut off from each other, other body tissues, and nutritive sources such as blood supply, and the usual inflammation response is absent.
Currently, treatments for cartilage repair are less than satisfactory, and rarely restore the necessary function nor return the tissue to its native normal state. Artificial cartilage prepared from cultured chondrocytes offers promise as a treatment for cartilage defects, but connecting this artificial soft tissue to bone in the attempts to restore the defected cartilage is difficult.
In the attempts to replace cartilage, most research involves the combination of in vitro expansion of chondrocytes with three-dimensional (3-D) synthetic or natural polymer scaffolds. Constructs have been comprised of materials such as polyglycolic acid, polylactic acid, various co-polymers, as well as natural materials of polysaccharides and collagen, and extracellular matrix proteins and hyaluronic acid constructs to mimic the natural in vivo environment.
Although the response of chondrocytes to these polymeric chemical constructs provided valuable information to advance the repair of chondral lesions, there are still complications to overcome. Problems have occurred such as acidic by product accumulation, local or systemic inflammatory reaction during in vivo degradation, and the degradation time is too short to allow neocartilage formation, leaving polymers less promising in clinical application. Furthermore, most of the polymers are lacking the dual functionality of osseointegration and cartilage growth, and do not always provide suitable mechanical properties needed to fully integrate with native bone tissue.